Node.js to TypeScript Converter

What changes when you move a Node.js project to TypeScript?

A working Node.js TypeScript project needs four things at once: ES Modules (or correctly typed CommonJS), explicit types on every exported function, a tsconfig.json with the right module resolution, and matching @types/* packages for your dependencies. Skip any one and the build fails.

JavaScriptConverter handles the first three deterministically. It reads each file as an AST, rewrites it to TypeScript, and reports the exact transforms it applied so you can audit the diff before merging.

Common Node.js patterns this tool rewrites

const express = require('express');
const app = express();

app.get('/users/:id', (req, res) => {
  res.json({ id: req.params.id });
});

import express, { Request, Response } from 'express';
const app = express();

app.get('/users/:id', (req: Request, res: Response) => {
  res.json({ id: req.params.id });
});

function requireAuth(req, res, next) {
  if (!req.headers.authorization) return res.sendStatus(401);
  next();
}
module.exports = requireAuth;

import { Request, Response, NextFunction } from 'express';

export default function requireAuth(req: Request, res: Response, next: NextFunction) {
  if (!req.headers.authorization) return res.sendStatus(401);
  next();
}

const { readFile } = require('fs/promises');

async function loadConfig(path) {
  const raw = await readFile(path, 'utf8');
  return JSON.parse(raw);
}

module.exports = { loadConfig };

import { readFile } from 'fs/promises';

export async function loadConfig(path: string): Promise<unknown> {
  const raw = await readFile(path, 'utf8');
  return JSON.parse(raw);
}

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "NodeNext",
    "moduleResolution": "NodeNext",
    "esModuleInterop": true,
    "strict": true,
    "skipLibCheck": true,
    "outDir": "dist"
  },
  "include": ["src/**/*"]
}

@types packages you'll likely need

JavaScriptConverter rewrites the source. The remaining step is installing the matching ambient type packages so the compiler knows the shape of each library. For a typical Express + Node 22 project that's:

npm install --save-dev typescript @types/node @types/express

Add @types/koa, @types/jest, or framework-specific packages as you need them.

Related framework migrations